This invention relates to processes for softening bonded nonwoven fabrics. More specifically, the invention relates to such processes wherein softening is effected by impingement of the fabric with a fluid jet.
Nonwoven fabrics and numerous uses thereof are well known to those skilled in the textiles art. Such fabrics can be prepared by forming a web of continuous filament and/or staple fibers and bonding the fibers at points of fiber-to-fiber contact to provide a fabric of requisite strength. The term "bonded nonwoven fabric" is used herein to denote nonwoven fabrics wherein a major portion of the fiber-to-fiber bonding referred to is adhesive bonding accomplished via incorporation of adhesives in the web to "glue" fibers together or autogenous bonding such as obtained by heating the web or by the use of liquid or gaseous bonding agents (usually in conjunction with heating) to render the fibers cohesive. In effecting such bonding, particularly autogenous bonding, the web may be subjected to mechanical compression to facilitate obtaining adequate bonding.
Nonwoven fabrics which are strongly bonded overall (for example, by uniform compression of the entire web in the presence of heat and/or appropriate bonding agents) tend to be stiff and boardy and are frequently more similar to paper that to woven textile fabrics. In order to obtain softer non-woven fabrics more closely simulating woven fabrics, nonwoven "point bonded" fabrics have been prepared by processes which tend to limit bonding to spaced, discrete areas or points. This is accomplished by application or activation of adhesive or bonding agent and/or application of heat and/or pressure at the points where bonding is desired. For example, the web to be bonded can be compressed between a pair of rolls or platens at least one of which carries bosses or a land and groove design sized and spaced to compress the web at the desired points. The compression means can be heated to effect thermal bonding of the web fibers or to activate a bonding agent applied to the web. In the actual practice of preparing point bonded fabrics, however, it is frequently difficult or even impossible to limit bonding to the desired points. In many processes web areas between the desired bond points are subjected to sufficient heat, compression, activated bonding agent or adhesive to effect "tack" bonding of fibers outside the desired bond points. Such tack bonding is believed to contribute significantly to undesired fabric stiffness.
It has been found that most point bonded nonwoven fabrics, particularly those having a large number of tack bonds, and many overall bonded nonwoven fabrics can be significantly softened by subjecting the fabric to mechanical stress. For example, the fabric can be washed in conventional domestic washing machines; drawn under tension over a sharply angles surface such as a knife blade; stretched; twisted; crumpled; or subjected to various combinations of such treatments. Such treatments are believed to effect softening primarily by breaking weaker fiber-to-fiber bonds such as tack bonds which can be broken without breaking the bonded fibers.
Although the softening techniques referred to above are relatively effective, they are subject to certain practical problems. For example, drawing a nonwoven fabric over a knife blade with sufficient force to effect substantial softening frequently results in undesirably high physical damage to the fabric. Washing of nonwoven fabrics in conventional washing machines generally yields quite good results with respect to softening. However, washing processes of this type are normally batch operations not readily adaptable for use in continuous processes of the type employed commercially for production of nonwoven fabrics.
It is apparent, therefore, that a commercially practical process for the softening of nonwoven fabrics would satisfy a long-felt need in the nonwoven textile art.